The present invention is a boost switching power converter. More specifically, the present invention is a converter for producing a DC voltage higher than that of the primary voltage source.
A common primary electrical power found in aircraft is either +28 volt DC (VDC) or three phase 115 volt AC (VAC), which is rectified and filtered to approximately 270 VDC. Many types of equipment have been designed to operate from either of these power sources.
Relatively small high power converters for changing the 115 VAC into +28 VDC have been known for some time. However, there has been a lack of small, efficient converters for changing +28 VDC into +270 VDC.
Boost converters have been used for some time to convert a low DC voltage into a higher DC voltage. A common boost converter includes an inductor, a diode, an output capacitor, and a power switching device. These converters for producing a voltage higher than the voltage of the primary source are sometimes referred to as "step-up" converters.
A common, known boost converter, or step up voltage converter, is shown in FIG. 1. Operation of the illustrated boost converter is well understood in the art. An input terminal 11 receives the input DC voltage (V.sub.in). An input capacitor 13 is connected between the input terminal 11 and ground. An inductor 21 having inductance L1 is connected to the input terminal 11. A switch, such as a Field Effect Transistor (FET) 41, is connected between the "output" side of the inductor 21 and a second terminal, such as ground. The switching element 41 is controlled by a regulator control 31. The regulator control 31 governs the time the switch is on (conductive) or off (nonconductive). A rectifying diode 61 couples the output side of the inductor 21 to the converter output terminal 81. The converter output voltage V.sub.out is produced on the converter output terminal 81. An output filter capacitor 91 is connected between the output terminal and ground.
When the FET 41 is conductive, energy from the input terminal 11 charges the inductor 21. When the FET 41 is not conductive, that energy is discharged through the diode 61 to charge the output capacitor 91. The regulator control 31 governs the ratio of the time the FET is conductive (on) and nonconductive (off) so that the output voltage V.sub.out on the converter output terminal 81 remains constant. The regulator control adjusts the on/off cycle of the switch 41 by monitoring the voltage on the converter output terminal 81 through a feedback line 35.
The voltage rating of the switching transistor 41 is determined by the peak voltage that will appear across the transistor when the regulator control 31 turns the transistor off, as the inductor 21 flies up to the output voltage, plus whatever overshoot may be present due to unwanted parasitic elements. With allowance for some derating for safe applications, a boost converter with an output voltage V.sub.out of 270 VDC requires a switching FET capable of carrying a voltage of at least 400 volts across its drain and source (a V.sub.DS rating of at least 400 volts).